1. Industrial Field of the Invention
The present invention relates to a display device and an electronic apparatus using the same and, in particular, to a reflection type liquid crystal display device which effects display by reflecting external light, and a transflective display device capable of being used both as a reflection type display device which effects display by reflecting external light and as a transmission type display device which effects display by transmitting light source light, and an electronic apparatus using the same.
2. Description of the Related Art
Hitherto, display devices using a liquid crystal panel have been of two types: reflection type display devices which effect display by using external light, and transmission type display devices in which light is applied from behind a liquid crystal panel.
In the case of a reflection type display device, the quantity of light is reduced in a dark place, so that the display is hard to see. In the case of a transmission type display device, the power consumption increases in proportion to the light source regardless of whether the place is light or dark, so that it is not particularly suitable for a portable display device or the like operated by a battery.
In view of this, a transflective display device is available, which can be used both as a reflection type and as a transmission type. In this display device, when it is used in a light place, external light impinging upon the display screen is reflected by a reflection plate provided inside the device, and while doing so, the quantity of light emitted from the display screen is controlled for each pixel by using optical elements such as a liquid crystal and a polarizing plate arranged in the optical path to effect reflection type display.
On the other hand, when this display device is used in a dark place, light source light is applied from the back side of the liquid crystal panel by a built-in light source such as a backlight, and while doing so, the quantity of light emitted from the display screen is controlled for each pixel by using the above-mentioned optical elements such as the liquid crystal and the polarizing plate to effect transmission type display.
Further, in a display device which can be used as both a reflection type and a transmission type device, TN (twisted nematic) liquid crystal, STN (super-twisted nematic) liquid crystal or the like is used for the liquid crystal with which the liquid crystal panel is filled, and according to the presence or absence of voltage applied to the pixels, the polarization axis of the liquid crystal is rotated to make the transmission polarization axis variable.
Further, the polarizing plate allows light having a linear polarization component in a predetermined direction to be transmitted therethrough.
Here, a conventional transflective display device will be described with reference to FIG. 10.
In FIG. 10, numeral 5110 indicates a voltage application region of a TN liquid crystal panel, and numeral 5120 indicates a voltage non-application region of the TN liquid crystal panel.
Numeral 5130 indicates an upper polarizing plate, numeral 5302 indicates an upper glass plate, numeral 5304 indicates a lower glass plate, numeral 5160 indicates a reflection polarizing plate, numeral 5307 indicates a semi-transmissive light absorbing plate, and numeral 5210 indicates a light source.
First, a case will be described in which black and white display is effected through reflection type display.
Incident light 5601 coming from the exterior of the display device is turned into light having a linear polarization component parallel to the plane of the drawing by the upper polarizing plate 5130, turned into light having a linear polarization component in a direction perpendicular to the plane of the drawing whose polarizing direction is twisted by approximately 90 degrees by the voltage non-application region 5120 of the TN liquid crystal panel, reflected by the reflection polarizing plate 5160 as light having a linear polarization component in a direction perpendicular to the plane of the drawing, again turned into light having a linear polarization component parallel to the plane of the drawing whose polarizing direction is twisted by approximately 90 degrees by the voltage non-application region 5120 of the TN liquid crystal panel, and emitted from the upper polarizing plate 5130. Thus, when no voltage is applied to the TN liquid crystal panel, white display is effected.
On the other hand, incident light 5603 coming from the exterior of the display device is turned into light having a linear polarization component in a direction parallel to the plane of the drawing by the upper polarizing plate 5130, transmitted as light having a linear polarization component parallel to the plane of the drawing without changing the polarizing direction by the voltage application region 5110 of the TN liquid crystal panel, and then absorbed by the semi-transmissive light absorbing plate 5307, with the result that black display is effected.
Next, a case will be described in which black and white display is effected through transmission type display. Light 5602 from the light source 5210 is transmitted through an opening formed in the semi-transmissive light absorbing plate 5307, turned into light having a linear polarization component in a direction parallel to the plane of the drawing by the reflection polarizing plate 5160, turned into light having a linear polarization component perpendicular to the plane of the drawing whose polarizing direction is twisted by approximately 90 degrees by the voltage non-application region 5120 of the TN liquid crystal panel, and absorbed by the upper polarizing plate 5130 to effect black display.
On the other hand, light 5604 from the light source 5210 is transmitted through the opening formed in the semi-transmissive light absorbing plate 5307, turned into light having a linear polarization component in a direction parallel to the plane of the drawing by the reflection polarizing plate 5160, and transmitted through the voltage application region 5110 of the TN liquid crystal panel as light having a linear polarization component in a direction parallel to the plane of the drawing without changing the polarizing direction to effect white display.
Generally speaking, in a display device using a liquid crystal panel, the thickness of the liquid crystal layer is as small as 5 to 10 μm. In contrast, the thickness of the substrate is 0.3 to 0.7 mm, which is very large as compared with the thickness of the liquid crystal layer.
Thus, when reflection type display is performed by using the above-described conventional display device, there is a marked difference in the optical path in the liquid crystal layer of the external light coming from above the liquid crystal panel between going and returning paths. Thus, depending upon the angle of incidence of the external light impinging upon the liquid crystal panel, the pixel that the external light passes in the going path differs from the pixel it passes in the returning path. When this difference in optical path is observed obliquely by the observer, a shadow is generated in the display in the case of black and white display, in which no color filter is used. This phenomenon is called parallax. In a display device using a color filter of a plurality of colors, the color the light passes in the going path differs from the color it passes in the returning path, resulting in color mixing.
While in the above-described prior art only a transflective display device has been shown, such problems are equally involved in a reflection type display device formed by removing the light source 5210 from the display device of FIG. 11 and replacing the semi-transmissive light absorbing plate 5307 by a light absorbing plate.
It is the first object of the present invention to provide a reflection type or a transflective display device in which a reduction is achieved in terms of parallax and color mixing generated in reflection type display.
Further, in the conventional transflective display device shown in FIG. 10, the semi-transmissive light absorbing plate 5307 is adopted, so that when effecting transmission type display, a part or the major part of the light emitted from the light source 5210 is absorbed by the semi-transmissive light absorbing plate 5307. Thus, the light emitted from the light source 5210 cannot be effectively utilized to a sufficient degree, with the result that the display is rather dark.
It is the second object of the present invention to provide a display device in which the light emitted from the light source is effectively utilized and which is capable of effecting bright transmission type display.
Further, in the above-described display device using a reflection polarizer, positive display is effected at the time of reflection type display and negative display is effected at the time of transmission type display based on the above display principle, resulting in a so-called positive/negative inversion.
It is the third object of the present invention to prevent this positive/negative inversion in a transflective display device using a reflection polarizer.